High power vacuum tube with magnetic beaming



Jan. 23; 1968 y H DOOUTTLE 3,365,601

HIGH POWER VACUUM TUBE WITH MAGNETIC BEAMING Original Filedqan. 28, 1965Y 3 Sheets-Sheet 1 W2 Q F53 I P J t 60 INVENTOI? HOWARD D. 000L/ 7 7' LEJ 1968 H. D. DQOLITTLE 3,

HIGH POWER VACUUM TUBE WITH MAGNETIC BEAMING Original Filed Jan. 28,1965 3 Sheets-Sheet 2 lNl/E/VTOI? HOW 1 RD 0 DOOL TTLE Jan. 23, 1968 H;D. DOOLITTLE 3,365,601

HIGH POWER VACUUM TUBE WITH MAGNETIC BEAMING Original Filed Jan. 28,1965 I BSheets-Shes 3 CONSTANT GRID-VOLTAGE CHARACTERISTICS er"=7.6 v oLTS PLATE CURRENT 5 GRID CURRENT----- I C=PEAK POSlTlVE 6 I400 GRIDVOLTAGE 'F/ae 4 PEAK PLATE CURRENT AMPERES PEAK GRID CURRENT AMPERES oO'I-23456789l0 PLATE VOLTAGE KILOVOLTS llVl/E/VTOR HOW/1D [7. DOOL/TTLEUnited States Patent 3,365,601 HlGH POWER VAQUUM TUBE WITH MAGNETEQBEAJVHN'G Howard D. Doolittle, Stamford, Conn, assignor to The MachlettLaboratories, incorporated, Springdale, Conn, a corporation ofConnecticut fiontinnation of application Ser. N 428,687, Jan. 2% 15 65.This application Fan. 24, 1967, Ser. No. 611,474 12 Claims. (6i. 313-21)ABSTRACT (PF THE DISCLOSURE An electron discharge device employingmagnetic fields for eifecting controlled how of electrons and comprisingan electrode structure embodying an anode having an open ended cavitytherein, an array of cathode filaments within the cavity, grid wires inthe cavity on either side of said filament array, and a magnet enclosingsaid anode.

This application is a continuation of application Ser. No. 428,687,filed Ian. 28, 1965, and now abandoned.

This invention relates to electron discharge devices and has particularreference to novel high power electron tube structures employingmagnetic fields for eifecting controlled fiow of electrons to preventproduction of grid current.

In the manufacture of high power tubes requiring emission from a cathodeof extremely large numbers of electrons, a serious problem has prevaileddue to the fact that critical control of electron flow is necessary toprevent electron impingement upon grid elements with resultantproduction of undesirable grid current. Such control in the past hastaken many forms, among them being specially shaped cathode structures,shielded grid structures, deflecting electrodes, and other meansdesigned to beam the flow of electrons between cathode and anode bycreation of appropriately shaped electric fields whereby the electronswill reach the anode without being substantially intercepted by gridelements and without substantial bunching at the anode.

Grid current is undesirable since it increases the drive power requiredto operate the tube, raises the grid temperature, and producesrelatively large secondary electron emission from the grid. The drivingpower for a tube is a product of the grid voltage swing and the gridcurrent. Except for circuit losses, the driving power may be reduced tozero if the grid intercepts no electrons and produces no grid current atall. Since in the presently described tube structure grid current isreduced by a factor of 10 or more over that of a conventional triode,the driving power is also reduced by the same order of magnitude. Inpower triodes a serious power limitation is due to high gridtemperatures. Current to the grid heats the grid wires. If the gridwires get too hot they can act as primary emitters and cause excessiveplate dissipation, as Well as loss of grid control. By substantiallyreducing the current produced in the grid, this problem is solved. Mosttriodes show regions of reverse grid current due to secondary electronemission from the grid. This can cause loss of control by the grid,resulting in pulse stretching in pulse modulator tubes and/or flasharcing to the plate. In general, this can be counteracted only byputting a resistor in parallel with the grid and cathode such that thecurrent in this swamping resistor is greater than the reverse gridcurrent. Obviously, the input resistor absorbs power from the drivingstage, and it is desirable to keep this resistor as large as possible.In tubes such as described herein, the secondary emission current ismuch smaller than in conventional tubes, since it is directly related tothe current produced in the grid by interception of electrons from thecathode. Furthermore, the magnetic field will tend to return somesecondary electrons to the grid.

Grid current produces secondary emission effects which sometimes resultin pulse stretching in conventional tube structures. This and otherdisadvantages are overcome in the presently described tube wherein gridcurrent is reduced by magnetically beaming electron flow so that it willnot be substantially intercepted by the control grid elements.

While magnetic beaming of electron flow in electron tubes has beenexplored in the past, this has been done in connection with relativelylow power devices and has not been heretofore successful when utilizedin high power pulse modulator, amplifier or oscillator tubes capable ofdelivering from up to seventy mw. of pulse output at 1200 amperes withpulse widths up to 10,000 microseconds or 2.5 mw. of CW power atfrequencies up to 30 inc. Tubes capable of high power performance havebeen made with complicated electrode structures for the purpose ofbeaming the electron flow from specially designed cathodes and gridstructures to the anodes, and generally included shield grid structureswhich were operated at cathode potential in order to achieve efiicientoperation.

The present invention achieves the described ellicient high poweroperation with a simple triode 0r tetrode structure utilizing simpleuncomplicated wire-like electrodes by virtue of magnetic electronfocusing together with novel and efiicient liquid cooling. This isaccomplished by the novel combination of an annular array oflongitudinally extendin" cathode filament wires, which array is locatedbetween two or four annular arrays of control grid wires. The grids andcathode are themselves both located between inner and outer annularanodes so that electron emission from the filaments may pass in bothdirections radially onto one or the other of the anodes. Beaming isefiected by a magnetic field extending radially of the tube from onepole of a magnet inside the inner anode to a second pole encircling theouter anode, and cooling is achieved by encircling the magnet andelectrode structures with a water jacket through which a coolant isintroduced into the interior of the tube around the anode as well asaround the magnet for efliciently dissipating heat. This combination offeatures, together with the novel cathode and grid structures, resultsin the production of a novel but simple tube structure which achievesthe desired exceedingly high power output.

These and other novel features of this invention will become apparentfrom the following description taken in connection with the accompanyingdrawings, wherein:

FIG. 1 is a front elevational view of a tube embodying the invention;

2 is a vertical sectional view talren substantially along the axis ofthe tube of FIG. 1;

PEG. 3 is a fragmentary view of the cathode and electrode structures ofthe tube;

FIG. 4 is an enlarged fragmentary sectional view of the devicesconnecting the cathode and grid electrodes to supporting decks;

PEG. 5 is a fragmentary view of cathode and grid wires arranged as in atetrode structure; and

FIG. 6 is a graph showing plate and grid currents for various plate andgrid voltages.

Referrin more particularly to the drawings wherein like characters ofreference designate like parts throughout the several views, the tubestructure embodies an annular metal anode 1i) (FIG. 2), preferably ofcopper, which is provided with an axially extending channel 11throughout the annulus, thus forming inner and outer annular walls 12and 33 respectively. The open mouth of the channel l]. is directedtoward the terminal structure to 7 heavy rugged ring to be usedadditionally as a support for mounting the tube in a coolant jacket, aswill be described later.

Depending into the cavity within the anode walls is a plurality ofthcriated tungsten filaments 17 forming part of an assembled cathodeelectrode structure 15.

Qathode structure 1% comprises a pair of axially spaced supporting rings18 and 19 which are connected at their inner peripheries to respectiveconcave decks 29 and 21. As can be seen best in FIG. 4, supporting rings18 and 19 are connected together but are insulated from each other by anintermediate ceramic spacer ring 22. A screw 23 or the like ispreferably used as a connecting member and is mounted in ring 19 whilebeing suitably insulated from ring 18. Rim 18 is preferably flanged asshown and is attached to deck ill by the flange.

As shown best in FIG. 3, the filaments 17 are U-shaped wires, preferablyof thoriated tungsten, mounted at the ends in the ends of elongatedstuds 24 and 24a respectively. Studs 24a extend through supporting ring1% into ring 18 to which they are conductively affixed, while studs 12dterminate at and are fixed to ring 19. Thus, filament power can beapplied to the filaments from one ring, through the respective studs andfilament wire, and then through the other studs to the second ring.Copious emission of electrons from the filaments will result.

lhe inner deck 21 is of relatively thick heavy metal such as copper andhas a central opening 25. One end of a tubular metal support as issealed to this deck adjacent the periphery of opening 25, as shown inFIG. 2, Outer deck 20 likewise has a central opening .27 and one end ofa second tubular metal support 28 is fixed thereto adjacent theperiphery of opening 27, support 28 encircling support 26 in spacedrelation thereto. The opposite end of support 2% extends toward theadjacent end extremity of the tube and with encircling terminal ring 29forms a cathode terminal to which may be attached means for supplyingpower to the filament. The inner support 26 extends only part way alongthe length of outer support 23 and is mounted on and supported bysupport 28 through an insulating seal comprising a pair of metal rings3d and 31 connected together by a ceramic ring 32, one metal ring 36being sealed to the extreme end of support 26 and the other ring 31being sealed to a metal ring 33 which is carried by the inner surface ofsupport 28. To provide a second cathode connection, a metal disc 34 issealed at its periphery to the inner surface of support 2:; and has acentral opening in which is fixed one end of a hollow elongated exhausttubulation 35, the other end of tubulation 35 being capped as at 36.During tube processing the interior of the vacuum chamber may beoutgassed through tubulation 35 and sealed off by cap 36, after whichthe cap and tubulation provide a second terminal means for connection ofthe second side of the cathode circuit to the external source of cathodepower (not shown).

The cathode structure becomes severely heated during operation of thedevice, and the resultant thermal expansion sometimes causes movement ofthe decks 29 and 21 with respect to one another, thus resulting inbowing of the filament wires as a result of shifting of one end of awire with respect to its other end. To overcome this problem,cathode-supporting deck as is made relatively thin and flexible and isclamped to deck 21 as described so that upon thermal expansion of theelements of the cathode the deck 29 will flex without affecting thefilament Wires.

The filaments 17 are so disposed as to lie in an annular arrangementthroughout the length of the annular cavity 11 in the anode, with eachside of the filaments lying equidistant from the axis of the tube. Agrid electrode 37 is provided and includes a plurality of U-shaped gridvires 38 of molybdenum or other selected metal, one grid wire 33 beingassociated with each filament wire 17 but at right angles thereto andmidway thereof as shown best in FlG. 3. Grid wires 38 are longer thanfilament wires 17 and extend slightly beyond wires 17 as shown, and aremaintained in preset spaced relation by a concave hoop 39 to' which theouter ends are attached. The opposite ends of grid wires 38 are mountedon adjacent ends of respective inner and outer supporting sleeves 40 and41 respectively Outer sleeve 41 has its other end conductively connectedto a frusto-conical supporting deck 42, the inner peripheral portion ofwhich is mounted upon a tubular grid support 43. Grid support 43encircles cathode support 28- in spaced relation therewith and isconnected to a grid terminal structure which includes a heavy metal ring44 sealed to the end thereof and a frusto-conical flanged metal terminalmember 45 which is disposed to flare outwardly therefrom, as shown bestin FIG. 2, for ease in attaching external means (not shown) forsupplying grid potential.

The inner grid sleeve 4% is mountedon a rigid ring 4-6 which is in turnsupported by studs 47 carried by grid-supporting ring 42, the studsextending freely through slots or openings in cathode-supporting rings20 and 21 to prevent shorting therewith.

The tube envelope encloses the grid and cathode supporting structuresand comprises a hollow insulating ceramic cylinder 48 attached at oneend by a kovar ring 49 to the grid terminal 45 and at the other end by aseries of ring seals 59, 51, 52, and 53 to the terminal end portion ofthe anode ill.

From the foregoing it can be seen that the tube utilizes a cathode whichcomprises a cylindrical array of axially disposed thoriated tungstenwires, preferably one hundred ten in number. The grid is ellectivelycomprised of an inner cylindrical array of axially extending wires on asmaller diameter than the cathode wires, and an outer array of largerdiameter than the cathode wires, whereby each set of grid wires isradially disposed midway between each of a set of cathode wires. A novelanode structure is provided for effectively placing two anodes insurrounding relation to the grids, one on a smaller inner diameterandthe other on a larger outer diameter.

Electrons emitted from the filament wires 17 will be drawn, under theinfluence of the grid wires 33, from the filaments toward the anodeportions 12 and 13. However, since in normal tube operation electronsare emitted from all sides of the filament wires, many thereof willimpinge upon the grid wires, causing undesired grid current, griddissipation and secondary emission eflects which sometimes result inpulse stretching. To overcome this undesirable condition, the presentlydescribed tube is provided with means for providing a magnetic field inthe intended direction of electron flow, that is, radially of the tubesaxis. To achieve this, there is provided an annular magnet 54 with acentral annular cavity 55 in which is suspended the anode structure 10.The portions 56 and 57 of the magnet forming the inner and outer wallsof the cavity comprise the north and south pole pieces of the magnet.Thus, the magnet flux extends radially of the pole pieces and,consequently, also extends in the directions of electron fiow. Thismagnetic field thus beams electrons from each cathode filament wire,directing the electrons in beams radially toward each anode section 12and 13 without substantial impingement of the electrons upon the gridwires.

The anode and magnet structures are located within an enclosing jacketthrough which water or other selected coolant is made to flow forcooling purposes. The jacket comprises a cylindrical outer side wall 58which is closed at one end by a base 59 and has a flange 60 at its otherend by which it may be bolted or otherwise secured in leakproof fashionto the anode terminal 15. Coolant is introduced from a suitable source(not shown) through one of a pair of pipes 61 directly into a cavity 63provided at the base of the magnet 54 by means of a U- shaped section inannular conduit 64, from which it is urged through openings 65 in magnet54 to the anode 10, as shown by arrows in FIG. 2. The coolant flowsupward over the entire outer surface of the anode l and then down aroundthe outer surface of the magnet 54 into the space 65 between the jacketconduit 64 and base 59, from which it is expelled through pipe 62. Thus,the magnet has been made to become part of the means for controllingflow of coolant in a manner to efliciently cool the heated elements ofthe tube. An inner cylindrical jacket wall 67 is suitably sealed at itsinner end as by ring 68 to anode disc 14 and at its outer end by a metalbellows 69 and disc 70 to complete the jacket enclosure. The spacewithin the wall '67 may be utilized to house a vac-ion pump or otherassociated equipment, if desired.

The tube described in the foregoing has been found to operate veryefficiently at DC plate voltage of 65 v. By operating at a tube drop ofkv., the plate eificiency is 92%. The cutoff [A is 20, which requires abias voltage of -3500 to 4000 volts. A positive grid drive voltage of3009 volts will give a plate current of 1150 amps. at 5 kv. tube drop.Grid current is less than 15 amps. This tube is capable of CW operationin excess of 2.5 mw. or pulsed RF. operation up to mw. at high duty.Filament power requires 7.6 volts at 1900 amperes or slightly less thankw. Since primary grid current is low, secondary emission effects areeasily neutralized.

Although the foregoing description specifically describes a triode tubestructure, the present invention is as readily adaptable to a tetrodestructure utilizing a second or screen grid comprising a number ofU-shaped wires 7i (FIG. 5) radially aligned with and straddling thecontrol grid wires 38a, the legs Tia and 71b of wires 71 being locatedin two respective annular configurations, one on either side of the grid38a between it and the opposed sides of the anode portions. This secondgrid may be operated at a positive DC potential of, for example, from2000 to 4006 volts or may be operated at ground potential in a shieldedgrid triode. The [1. of this grid with respect to grid 37 would be ofthe order of five. Such a structure would possess the usual desirablecharacteristics of conventional tetrodes over conventional triodes, suchas reducing the control grid swing necessary to extract maximumpermissable current from the cathode and substantially reducing thecapacitance between the plate and control grid. This latter feature isof particular importance at frequencies above a few megacycles on tubesof this size. Conven tional screen grid tetrodes are limited in poweroutput by screen grid dissipation. However, a magnetic field tetrode asdescribed herein will substantially reduce the screen grid dissipationand permit higher power output.

An additional interesting and advantageous feature relating to magneticfield electron beaming is that the magnetic field acts to opposespreading or contraction of the electron beam. That is, in thecathode-to-grid area, the magnetic field restricts beam spreading. itthe beam normally tends to focus on a localized anode area bycontraction, the magnetic field will tend to widen the beam. In triodesusing electrostatic beaming, there are a certain set of plate and gridvoltages which cause sharp focusing of the beam on the anode, givingrise to high power density on restricted anode areas and leading toexcessive local anode temperatures. This type of undesirable focusing isopposed in a magnetic structure.

From the foregoing, it will be apparent that a novel high power electrontube has been achieved. It will also be apparent that many modificationsand changes may be made in the structures and methods described by thoseskilled in the art. Accordingly, it should be understood that theforegoing description is illustrative only and should not be interpretedin a limiting sense.

I claim:

1. A high power electron discharge device comprising an envelope, anannular anode connected at one end to the envelope and having an annularopen-ended cavity therein, an annular array of cathode filamentsextending within said cavity, a pair of annular arrays of grid wiresextending into said cavity one on either side of said filament array,terminals connected to said filaments and grid wires extendingexternally of said envelope, and an annular magnet enclosing said anode,the magnet having inner and outer walls defining an annular cavitywithin which the anode is suspended, the inner and outer walls of themagnet being pole pieces influencing flow of electrons radially fromsaid filaments to said anode.

2. A high power electron discharge device comprising an envelope, anannular anode connected at one end to the envelope and having an annularopen-ended cavity therein, an annular array of cathode filamentsextending within said cavity, a pair of annular arrays of grid wiresextending into said cavity one on either side of said filament array, apair or" substantially parallel filamentsupporting decks, the filamentsbeing connected at 0pposite ends to respective decks, terminal membersextending from respective decks and from said grid wires externally ofthe envelope, and an annular magnet enclosing said anode, the magnethaving inner and outer walls defining an annular cavity within which theanode is suspended, the inner and outer walls of the magnet being polepieces influencing flow of electrons radially from said filaments tosaid anode.

3. A device as set forth in claim 2 wherein one of said decks is rigidand the other is flexible, said flexible deck comprising means formaintaining the filaments stress free under conditions of varyingtemperature.

4. A high power electron discharge device comprising an envelope, anannular anode connected at one end to the envelope and having an annularopen-ended cavity therein, an annular array configuration of cathodefilaments extending within said cavity, a pair of annular arrays of gridwires extending into said cavity one on either side of said filamentarray, terminals connected to said filaments and grid wires extendingexternally of said envelope, said filaments comprising wires formedsubstantially in U-shapes and disposed in planes extending substantiallyin the arc described by said annular configuration, said grid wires eachdefining a U-shaped configuration and each disposed in a plane radiallyof the device and substantially at right angles to the planes of thefilament wires, and an annular magnet enclosing said anode, the magnethaving inner and outer walls defining an annular cavity within which theanode is suspended, the inner and outer walls of the magnet being polepieces influencing flow of electrons radially from said filaments tosaid anode.

' the envelope and having an annular open-ended cavity therein, anannular array of cathode filaments extending Within said cavity, deckssupporting respective opposite ends of the filaments, a pair of annulargrids extending into said cavity one on either side of said filamentarray, said grids each composed of U-shaped wires, the respective legsof which comprise parts of respective grids, the U-shaped wires eachbeing disposed in a plane extending radially of the device, a decksupporting one of said grids, a ring supporting the other grid, meansextending through said filament-supporting decks mounting the ring onthe grid-supporting deck, terminals connected to said decks extendingexternally of said envelope, and an annular magnet enclosing said anode,the magnet having inner and outer walls defining an annular cavitywithin which the anode is suspended, the inner and outer walls of themagnet being pole pieces influencing flow of electrons radially fromsaid filaments to said anode.

6. A high power electron discharge device comprising an envelope, anannular anode connected at one end to the envelope and having an annularopen-ended cavity therein, an annular array of cathode filamentsextending within said cavity, a pair of annular arrays of grid wiresextending into said cavity one on either side of said filament array,terminals connected to said filaments and grid wires extendingexternally of said envelope, an annular magnet enclosing said anode, themagnet having inner and outer walls defining an annular cavity withinwhich the anode is suspended, the inner and outer walls of the magnetbeing pole pieces influencing flow of electrons radially from saidfilaments to said anode, and means for cooling said anode comprising ajacket enclosing the sides and one end of said magnet in spaced relationtherewith, inlet and outlet means connected to said jacket, and meansfor directing coolant from said inlet means through the magnet onto'theanode and thence along the outer surface of the magnet to the outletmeans.

7. A high power electron discharge device comprising an envelope, ananode connected at one end to the envelope and having a cavity therein,an array of cathode filaments extending in a linear fashion Within saidcavity, a pair of arrays of grid wires extending into said cavity one oneither side of said filament array, terminals connected to saidfilaments and grid wires extending externally of said envelope, and amagnet enclosing said anode and defining a cavity within which the anodeis suspended, opposed side walls of the magnet being pole piecesinfluencing flow of electrons transversely from said filaments to saidanode.

8. A high power electron discharge device comprising an envelope, ananode connected at one end to the envelope and having a cavity therein,an array of cathode filaments extending within said cavity, a pair ofarrays of grid wires extending in a linear faslr'on into said cavity oneon either side of said filament array, a pair of substantially parallelfilament-supporting decks, the filaments being connected at oppositeends to respective decks, terminal members extending from respectivedecks and from said grid wires externally of the envelope, and a magnetenclosing said anode and defining a cavity within which the anode issuspended, opposed side walls of the magnet being pole piecesinfluencing flow of electrons transversely from said filaments to saidanode.

9. A device as set forth in claim 8 wherein one of said decks is rigidand the other is flexible, said flexible deck comprising means formaintaining the filaments stress free under conditions of varyingtemperature.

10. A high power electron discharge device comprising an envelope, ananode connected at one end to the envelope and having a cavity therein,an array of cathode filaments extending within said cavity, a pair ofarrays of grid wires extending into said cavity one on either side ofsaid filament array, terminals connected to said filaments and gridWires extending externally of said envelope, said filaments comprisingWires formed substan tially in U-shapes and disposed in planes extendingsubstantially in a predetermined configuration, said grid wires eachdefining a U-shaped configuration and each disposed in a planesubstantially at right angles to the planes of the filament wires, and amagnet enclosing said anode and defining a cavity within which the anodeis suspended, opposed side walls of the magnet being pole piecesinfiuencing flow of electrons transversely from said filaments to saidanode.

11. A high power electron discharge device comprising an envelope, ananode connected at one end to the envelope and having a cavity therein,an array of cathode filaments extending within said cavity, deckssupporting respective opposite ends of the filaments, a pair of gridsextending into said cavity one on either side of said filament array,said grids each composed of U-shaped wires, the respective legs of whichcomprise parts of respective grid elements, the U-shaped Wires eachbeing disposed in a plane extending transversely of the filament array,a

deck supporting one end of said grids, a support for the other end ofthe grid, means extending through said filament-supporting decksmounting the support on the gridsupporting deck, terminals connected tosaid decks ex-. tending externally of said envelope, and a magnetenclosing said anode and defining a cavity within which the anode issuspended, opposed sides of the magnet being pole pieces influencingflow of electrons transversely from said filaments to said anode.

12. A high power electron discharge device comprising an envelope, ananode connected at one end to the envelope and having a cavity therein,an array of cathode filaments extending within said cavity, a pair ofarrays of grid wires extending into said cavity one on either side ofsaid filament array, terminals connected to said filaments and gridwires extending externally of said envelope, a magnet enclosing saidanode and defining a cavity Within which the anode is suspended, opposedsides of the magnet being pole pieces influencing flow of electronstransversely from said filaments to said anode, and means for coolingsaid anode comprising a jacket enclosing the sides and one end of saidmagnet in spaced relation therewithin, inlet and outlet means connectedto said jacket, and means for directing coolant from said inlet meansthrough the magnet onto the anode and thence along the outer surface ofthe magnet to the outlet means.

References Cited UNITED STATES PATENTS l,714,405 5/1929 Smith 313l6l2,332,977 10/ 1943 Skellet 3 13-162 2,496,003 1/1950 Eaves 313-2462,810,849 10/ 1957 Agule 313-45 DAVID J. GALVIN, Primary Examiner.

